Ms. Xuemei Wang dissertation defense on Integrated Grating couplers on-a-chip: characterizations and applications

Departmental News

Dr. Pinghan Chu

Posted: June 15, 2022

Date: Friday, July 1, 2022

Time:  9:00 AM - 10:30 AM

Location:  at CHTM, Room 101


Dr. Steven Brueck, Committee Chair, UNM ECE Department 
Dr. Payman Zarkesh-Ha, UNM ECE Department 
Dr. Tito Busani, UNM ECE Department
Dr. Tara Drake, UNM Physics Department 


In this dissertation, we demonstrate two applications based on grating coupled phase matching to a slab waveguide: lab-on-a-chip spectrometer using a transversely chirped grating and indoor lidar plenoptic sensor array for Time of flight (ToF) position mapping system. In the first application, a chirped grating waveguide coupler serves as a spatially dependent narrow-band filter. The transversely-chirped-input grating is fabricated on a SiO2-Si3N4-SiO2 waveguide atop a Si substrate by interferometric lithography in two sections on a single silicon substrate. Light with wavelength from 400- nm to 700 nm couples into Si3N4 waveguide through transversely chirped grating incident at a 33.5⁰ angle and is detected by a 2048-element linear CMOS detector array after coupling out from a fixed period grating. A wavelength dependent resolution of <1.6 nm is demonstrated across the visib le without any signal processing reconstruction.  This system can be made into an integrated optical solution with the detector and the signal processing electronics on the same silicon wafer, with a size as small as ~5 mm2. The goal of second application is to fabricate a time-of-flight sensor array based on grating-coupled waveguide looking in many different directions and covering a large azimuth/altitude footprint by standard microelectronic manufacturing. Light emitted by 940 nm VCSEL is scattered from objects and grating coupled into a slab waveguide. Light is coupled into one or more grating detectors and rejected by others due to phase mismatching with different grating periods and orientations. The acceptance angle of scattered light is determined by the waveguide properties and grating period/orientation of the detector. As the grating coupler works as narrow-band filter, the plenoptic sensor displayed a good immunity to background light sources. Devices were fabricated in a commercial foundry process, making this amenable to low-cost, large-scale manufacturing.